runeToLowerCase function Null safety

int runeToLowerCase(
  1. int rune
)

Convert a UTF32 rune to its lower case.

Implementation

int runeToLowerCase(int rune) {
  // Assume only Basic Multilingual Plane runes have lower and upper cases.
  // For other characters, return them as is.
  const int utf16BmpUpperBound = 0xD7FF;
  if (rune > utf16BmpUpperBound)
    return rune;
  return String.fromCharCode(rune).toLowerCase().codeUnitAt(0);
}